This novel mapping technique developed by Yasamin Mostofi allows two drones to map the interior of an unknown building by using wifi signals and some impressive number-crunching.
Via Mostofi's lab:
There are four tightly-integrated key components to our proposed approach to enable 3D through-wall imaging, as shown in the figure below. First, we have proposed robotic paths that can capture the spatial variations in all the three dimensions as much as possible while maintaining the efficiency of the operation. Second, we have modeled the 3D unknown area of interest as a Markov Random Field and utilized Loopy Belief Propagation to update the imaging decision of each voxel. In order to approximate the interaction of the transmitted wave with the area of interest, we have used the WKB linear wave model. Finally, we have also taken advantage of the compressibility of the information content to image the area with a very small number of WiFi measurements (less than 4%), using sparse signal processing.
More details about how it works here.